Action-selection perseveration in young children: Advances of a dynamic model.

This study presents an empirical test and dynamic model of perseverative limb selection in children of 14-, 24-, and 36-months old (N = 66 in total). In the experiment, children repeatedly grasped a spoon with a single hand. In two separate conditions, the spoon was presented either four times on their right side or four times on their left side. In both conditions, following this training, the spoon was presented on midline for two more trials. This setup enabled us to determine whether children's limb selection was influenced by their prior choices in the task (i.e., perseveration). Individual children's handedness was determined in a third condition consisting of nine object presentations (laterally or on midline). A dynamic model for limb selection is presented combining external input, motor memory, and preferences. The model was used to simulate the experiment and reproduced the results, including the age-related changes.

The significance of event information for 6- to 16-month-old infants' perception of containment.

Four experiments familiarized 6-, 9-, 12-, and 16-month-old infants to a solid block that was repeatedly lowered into a semitransparent container. In test trials the end state, containment, was either compatible or incompatible with the objects' size and position. In Experiment 1, infants saw the block and box successively before they observed the end state. This forced infants to attend to each object individually and memorize its size and position while observing the end state. In Experiments 2 and 3, the block and container were shown simultaneously, the block suspended above the container at a distance of either 25 cm (Experiment 2) or 2 cm (Experiment 3). The shorter distance made direct comparison easier to perform. In Experiment 4, the full event was shown in which the block was lowered inside the container from a distance of 25 cm. Infants' perception of containment was related to the visual information that was available. When the event made it easier to grasp the relevant information, infants could perceive whether the block could pass in the container at a progressively younger age.

Young children's use of a visual aid: an experimental study of the effectiveness of training.

We report an experiment concerning the use of a stand magnifier by young children with visual impairments (21 males, 12 females; mean age 4y 8mo [SD 11mo]). Children had a normative developmental level and a visual acuity of 0.4 or less (< or =20/50 in Snellen's notation). To measure magnifier use objectively, we developed a task that closely resembled the dynamics of its real-life (pre-reading) use. Children had to follow trails visually, from a start location to an unseen end location. This could only be done successfully and reliably by proper use of the magnifier. In addition to this, we analyzed the effect of specific training with the magnifier by using a repeated-measures (before and after training) matched-groups (with respect to age and near-visual acuity) design. Results established both the task's efficacy as an instrument for measuring magnifier use in young children and the effectiveness of the training. Improvement in task performance after training was found in both groups, except for the youngest children (<3y 6mo). On average, 1.8 times as many paths were followed in both groups after training (p=0.001). The without-magnifier training group became 2.5 times as good at finding the correct end location, whereas the with-magnifier training group became 4.3 times as good (p=0.05).

Occluding the trajectory of an object: effects on predicting containment with 9-, 12- and 16-month-olds.

Infants of 9-16-month-old repeatedly saw a block that was lowered into the opening of a container. It was found that the more time infants have to see the block relative to the container the easier they detect that the object relation specifies containment.

Action planning in young children's tool use.

Tool use consists of at least two coupled phases of activities, involving multi-step problem solving. It therefore provides an interesting window on the development of planning in goal-directed behavior. This study investigated 2-year-olds' and 3-year-olds' hand use in picking up and subsequently using a tool for displacing a target-object towards a specified goal location. The children had to use a stick (Experiment 1; N = 41 in total) or a cane (hooked stick) that was lying in varying starting orientations (Experiment 2; N = 32 in total). Age differences were found in the way goal-related information in combination with tool-related information influenced the choice of which hand to use in different phases of the task. A view on action planning is developed as a dynamic action-selection process for which actions to take. This process integrates factors that are internal to the child's action system (e.g. motor preferences and dexterity) with external (i.e. sensory) sources of information.

The planning of tool-to-object relations in young children.

This study investigated the way young children used a cane for displacing an object. In the experiment, 11 children with an average age of 32.3 months were asked to pick up a cane (hooked stick) that was located and orientated differently on each trial. With this cane they had to displace a target-object towards a free-to-choose goal location. The way the children used the cane for transporting the object was not determined by its starting location and orientation relative to the object. In fact, the children preferred enclosing the object in the hook, irrespective of the starting configuration. This contradicts a prediction that follows from an earlier study by Van Leeuwen et al. (1994). Final location of the target object and hand use was influenced by preferences as well as constraining task variables.

Variations of tool and task characteristics reveal that tool-use postures are anticipated.

The authors examined anticipation in tool use, focusing on tool length and tool-use posture. Adults (9 women and 9 men in each experiment) held a rod (length 0.4-0.8 m), with the tip upward; walked toward a cube; chose a place to stop; and displaced the cube with the rod's tip. In 2 experiments, rod length, mass, and mass distribution, and the size of the cube were manipulated. Chosen distance depended on rod length and cube size. Because effects of cube size on distance resulted only from postural changes related to required control, distance anticipated displacement posture. A postural synergy comprising legs and trunk provided a stable platform for the displacement. An arm synergy was less extended for small cubes, longer rods, and handle-weighted rods. Selected distance anticipated those postures.

Geometrics and dynamics of a rod determine how it is used for reaching.

Displacing an object with a hand-held rod provided a simple paradigm for studying tool use. The authors asked how reaching was affected by manipulations of rod properties. Adults held a rod (length =.10 to 1.5 m), with its tip in the air; walked toward an object on a table; chose a place to stop; and displaced the object with the rod's tip. In 3 experiments (Ns = 9, 22, and 17 participants), the authors manipulated rod length, mass, and mass distribution to determine whether and how geometric and dynamic properties affected the chosen distance and the posture. Both the chosen stopping distance and the postures were well accommodated to rod characteristics. Postural adaptations took place only in the arm, which was organized as a synergy. Predictably, rod length explained most of the variance, but small and reliable differences in both distance and posture depended on mass and mass distribution. The chosen distance anticipated not only rod length but also the upcoming posture needed to control the rod.